1. Field of the Invention
The present invention relates generally to a camera lens driving apparatus, and more particularly to a camera lens driving apparatus that is capable of presetting a focus position.
2. Description of Related Art
There is known a conventional lens apparatus for a TV camera, etc. that has a so-called focus presetting function of compulsorily moving or placing a focus lens from an arbitrary position to a previously-set focus position with one touch of a button.
Japanese Patent Provisional Publication No. 1-129579 discloses a TV camera apparatus, to which the focus presetting function is applied.
The conventional lens apparatus with the focus presetting function comprises a presetting switch for presetting a focus position and a return switch for compulsorily placing the focus lens to the preset focus position. If the setting switch is pressed, the present position of the focus lens is set as the preset focus position (which will hereafter be referred to as a preset position). If the return switch is pressed, the focus lens moves automatically from an arbitrary position to the preset position. Then, if the return switch is pressed again or if the focus demand is operated, the compulsorily-placing is cancelled so that the focus lens can move to a position designated by the focus demand.
If the compulsorily-placing is cancelled as stated above, the focus lens automatically moves to the position designated by the focus demand, and hence, the focus cannot be adjusted with respect to the preset position during the compulsorily-placing. For this reason, if the lens is out of focus at the preset position during the compulsorily-placing, the focus must be adjusted by the focus demand after the compulsorily-placing is cancelled. If this operation is performed during the broadcasting, a defocusing image is televised.
In order to solve the above-mentioned problem, it is possible to restart to move the focus lens with respect to the preset position by operating the focus demand after the focus lens is moved to the preset position under the compulsorily-placing. If a potentiometer, etc. determines the rotated amount of the focus demand as an absolute value, however, there is a problem difference between the position designated by the focus demand and the actual position of the focus lens because the focus demand has mechanical rotational ends. More specifically, there is a certain relationship between the rotational position of the focus demand and the position of the focus lens (they are usually proportional to one another), and the rotational ends of the focus demand usually correspond to the movement ends of the focus lens. If the focus demand can restart to move the focus lens from the preset position, a difference at the time of the compulsorily-placing between the position designated by the focus demand and the preset position remains after that. Thus, even if the focus demand is rotated to the rotational end, the focus lens cannot move to the movement end.